Measures of global biodiversity dynamics (past and present) are meaningless … or are they? Introductory comments

Abstract

One can argue that the critical factors in evolution are competitive interaction, dispersal, and survival in that they determine the life and death of individuals and thus govern gene flow and the waxing and waning of populations; the byproduct of this cascade happens to be the origination and extinction of species and phylogenetic lineages. Perhaps evolutionary “truth” can be found only in petri dish experiments of lichens competing for space, through documentation of the wildly successful ecological invasion of purple loosestrife in ditches of northeastern North America, or by molecular phylogeographic analyses of the distribution of fruit fly lineages across the Hawaiian Islands. Nonetheless, there is something fundamentally intriguing in the fact that there are some 300,000 species of angiosperms currently distributed around the planet; an order of magnitude greater than other, far more ancient clades such as cycads, ferns, and horsetails and a discrepancy that has spurred centuries of evolutionary theorizing on the causes of their high relative diversity—Darwin's “abominable mystery.” These sorts of macroevolutionary questions necessitate research agendas that target global distributions of taxa over long intervals of geological time. Did mammals stay low to the ground until the large-bodied herbivore niches were opened up when an asteroid knocked off the last of the non-avian dinosaurids at the end of the Cretaceous? Was the transition from the dazzling variety of trilobites that dominated Cambrian and Ordovician marine ecosystems to the diverse ammonoid fauna of the later Paleozoic associated with differing intrinsic taxonomic turnover rates? Are species in tightly integrated communities such as reefs more vulnerable to extinction during intervals of climate change than species with lower levels of ecological connectivity?